Known precursor solutions for the deposition of terbium based thin films are unstable, and must be used within a very short time after the precursor components are combined. Silicon oxide thin films have broad applications in many semiconductor industry areas. Silicon oxide thin films, with doping elements having specific properties, are of the greatest importance in many new devices. One example is a terbium-doped SiO2 thin film, which exhibits both photoluminescence and electroluminescence, has potential applications in the fabrication of electroluminescent devices.
There are many known techniques in use to fabricate an SiO2 thin film, such as PECVD, thermal oxidation, PVD and spin-coating. Each process produces a SiO2 thin film having different specific properties. For example, thermal oxidation processes produce a SiO2 thin film having extremely high uniformity and reliability, and is often used for fabrication of a gate oxide layer. The spin-coating process lends itself to composition adjustment for deposition of a SiO2 thin film doped with various impurities, such as terbium oxide.
Prior art SiO2 spin-coating precursor synthesis usually incorporate a TEOS (Si(OCH2CH3)4) component, which provides a source of silicon. However, TEOS is exceptionally volatile, and a single coating of TEOS-based SiO2 is too thin to be of much use, requiring multiple coating steps to build a usable SiO2 thin film. The incorporation of impurities, such as terbium, into a TEOS-based solution results in precipitate formation, which renders the solution unusable in spin-on applications.
A commercialized SiO2 spin-coating precursor solution, know as SOG (spin on glass) solution, produced by Dow Chemical Company, includes of a family of materials having silicon-oxygen (Si—O—Si) backbone structures. A detailed composition of SOG is not known, as the solution is proprietary to the manufacturer, so it is not known whether the commercialized SOG precursor is suitable for use in the method of the invention described and claimed herein.